those with three are WW. angelica Scott (1899), M. 
Thompsonu Andrews (1945), MM. endocentrica Baxter 
(1949), WW. pusilla Scott (1914), MM. elongata Baxter 
(1949) and JM. Noe: Steidtmann (1944): and that with 
four “‘steles’’ is M. centrofiis De Fraine (1914). The 
latter species is curious in possessing one small ‘‘star 
ring, flanked by three larger ‘‘steles’” (Plate LXTII, 
fig. 2). The second group consists of one form only, MW. 
primacva Baxter (1949), which possesses six to eight 
“*steles’” of varying size (Plate INT, fig. 8). 
In addition to exhibiting a presumably significant dif- 
ference in the number of unit ‘‘steles,’” JZ. Olseniae pre- 
sents a perhaps more significant character in the posses- 
sion of a central parenchymatous core devoid of ‘‘star 
rings” or other supernumerary vascular strands. Because 
of these two structural features, it seems desirable to pro- 
pose a new specific name tor the Wedullosa described in 
this study. 
Owing to its occurrence in post-Carboniferous sedi- 
ments, MW. Olseniae is of interest in the interpretation of 
phylogenetic trends in the Medullosan group. In com- 
parison with Permian representatives in western Europe 
it is surprisingly simple in structure, and may be inter- 
preted as structurally more primitive. However, it is 
difficult to incorporate MW. Olseniae into the phylogenetic 
schemes proposed for the American Carboniferous forms 
by Baxter (1949) and Stewart (1951). Until more is 
known of the possible variation within a single ‘*species”’ 
of Medullosa, however, phylogenetic schemes will proba- 
bly require periodic modification, 
[ 199 | 
